A wailing child, a needle-wielding doctor — what parent wouldn’t feel a twinge, at least for one heart-stopping moment, and wonder whether a shot is truly necessary at this moment?

Every year, vaccines prevent 6 million deaths worldwide, and numerous scientific studies have proven vaccines safe. Still, many parents have lingering worries about vaccines and consider ways to cut back the number or delay the timing of them. Here are the facts about vaccine safety and scheduling.